1. Field of the Invention
The present invention relates to an image reading apparatus in which two or more line image sensors are arranged in a width direction of a paper for the purpose of corresponding to a large-size paper, and more particularly to a method of adjusting a reading position and a method of reading an image for the purpose of reading an image having a good quality.
The present invention relates to an image reading apparatus employed for reading a large-size paper, and more particularly to an image reading apparatus provided with a light source for reading an image having a good quality.
2. Description of the Related Art
For example, an image reading apparatus provided in a copy machine or the like is provided with line image sensors structured such that photo-electric conversion elements such as a charge couple device (hereinafter, refer to as a CCD) or the like are arranged in a line in a main scanning direction, and reads an image in accordance with a scanning operation.
In a conventional line image sensor, a sensor which can correspond to a paper having a A3 size has spread, however, it has been impossible to manufacture a line image sensor having a size more than the above.
For example, a paper having an A0 size has a width of about 840 mm, in the case of reading a pixel in 400 dpi, 13230 pixels are required. On the contrary, the line image sensor is currently structured to only have about 7500 pixels, and accordingly, in order to correspond to the paper of A0 size, two line image sensors are required.
In view of the background mentioned above, in an apparatus of the type treating the large paper such as the A0 size or the like, there has been employed a method of reading an image by arranging two line image sensors in a line in a main scanning direction (a direction vertically crossing a paper supply direction and coinciding with a width direction of a paper) and combining the scanning operations of these line image sensors. This type of image reading is described, for example, in Japanese Patent Unexamined Publication No. 62-101170.
In a structure in which a plurality of line image sensors are arranged in addition to the structure described in this publication, it is necessary to partly overlap a reading area for adjacent line image sensors so as to prevent a joint portion from being generated in the image by a boundary portion between the adjacent image sensors. In accordance with the arrangement of the line image sensors, the image can be read from the large size paper.
The line image sensor is severely controlled in a manufacturing step, and is assembled in an apparatus main body so that a position shift or the like is not generated and shipped.
However, since the portion at which the line image sensors are overlapped becomes the joint portion of two image reading area, there is a possibility that the line image sensors are shifted from a normal position when a vibration or the like is applied to the line image sensors at a time of shipping or mounting. The position shift is generated in both of the main scanning direction and a sub scanning direction (a paper supply direction). Then, the position shift in the main scanning direction forms an image shift in a width direction of the paper, and the position shift in the sub scanning direction forms an image shift in the paper supply direction.
In order to prevent the image from shifting, it is necessary to detect and correct the position shift of the line image sensor. As the correcting method, for example, there is a method of cutting a chart corresponding to a marker receiving a light beam from an optical system provided in an image reading apparatus itself on a back surface of a platen for supporting the papers and detecting a position shift of the line image sensor with reference to the chart.
However, since the platen itself is fixed to the apparatus, it is very hard to accurately position the marker to a normal position due to an assembling error to the apparatus or the like even when the marker is provided on the back surface thereof. Accordingly, even when it is possible to detect the position shift of the line image sensor, it is hard to obtain an optimum value for quantitaively correcting, so that it is impossible to effectively restrict the image shift.
FIG. 17 is a schematic view of a reading optical system of a conventional image reading apparatus as seen in a main scanning direction.
In FIG. 17, an image forming apparatus is provided with a paper supply passage for a paper (not shown) in a direction of an arrow in FIG. 17 as setting a surface having an image to be read of the paper to be faced downward, and an image reading portion for scanning and reading the image on the paper passing over a target glass 11 provided in the paper supply passage. The image reading portion is provided with an optical system which irradiates a light beam onto the image surface of the paper over the target glass 11 from a light source 12, forms a reflected light beam by a lens 13 and enters into a line image sensor 14.
Here, a structure employed as the light source 12 includes a cold cathode tube or the like. A cold cathode tube having a longitudinal length substantially corresponding to a degree between an A4 size and an A3 size is developed. Further, since the cold cathode tube is strong against a low temperature and has a quantity of light between forty thousands and a hundred thousands which is more than that of LED and a fluorescent lamp, the cold cathode tube is suitable for a light source of a normal size image reading apparatus, for example, for the A3 size or the like.
However, in the case that it is desired to realize the image reading apparatus for treating the large size paper such as an A0 size or the like, since the cold cathode tube has only a length capable of corresponding to the A3 size, it is impossible to use the cold cathode tube as it is for the light source.
At this time, even when arranging the cold cathode tubes in a line in a main scanning direction and providing and using in a connecting state, a socket portion exists at both ends of the cold cathode tube and an effective irradiation range exists in the light source. Accordingly, a quantity of light in the connecting portion of the adjacent cold cathode tubes becomes insufficient.
Accordingly, an object of the present invention is to provide an image reading apparatus structured such that two or more line image sensors are arranged in a main scanning direction, in which it is possible to securely restrict a position shift of an image reading area caused by a line image sensor, thereby performing an image reading operation at a high quality.
Further, an object of the present invention is to provide an image reading apparatus which can irradiate a sufficient amount of light beam to a large-size paper and can perform a good image reading operation.
In accordance with the present invention, there is provided a method of adjusting an image reading position structured such that a plurality of line image sensors having CCDs arranged as a photo-electric conversion element are arranged in a main scanning direction of a paper, and end portions in respective reading areas of the line image sensors adjacent to each other in an arrangement direction are overlapped with each other, thereby adjusting an image reading position of the line image sensor at a time of reading a whole image on the paper by a combination of the line image sensors, comprising the steps of:
forming an image on an area included in the overlapping portion between a pair of adjacent line image sensors so as to form a marker;
respectively reading the marker by the pair of line image sensors;
inspecting a relative position of each of the pair of line image sensors with respect to the marker on the basis of each of output values of the pair of line image sensors at a time of reading the marker; and
coinciding each of the overlapping portions of the pair of line image sensors with a sub scanning direction on the basis of the inspected result of the relative position.
In accordance with the present invention, there is provided a method of reading an image structured such that a plurality of line image sensors having CCDs arranged as a photo-electric conversion element are arranged in a main scanning direction of a paper, and end portions in respective reading areas of the line image sensors adjacent to each other in an arrangement direction are overlapped with each other, thereby reading a whole image on the paper by a combination of the line image sensors, comprising a step of:
gradually changing the image in the overlapping portion between the line image sensors adjacent in the main scanning direction from an image data main body of the image read by one of the line image sensors to an image data main body of the image read by another of the line image sensors, toward the main scanning direction.
In accordance with the present invention, there is provided an image reading apparatus structured such that a plurality of line image sensors having CCDs arranged as a photo-electric conversion element are arranged in a main scanning direction of a paper, and reading areas of the line image sensors adjacent to each other in an arrangement direction are overlapped with each other, comprising:
moving means for independently moving each of the line image sensors in a sub scanning direction vertically crossing the main scanning direction;
image forming means for forming an image on an area included in the overlapping portion between the line image sensors so as to form a marker;
inspecting means for inspecting a relative position of each of the pair of line image sensors with respect to the marker on the basis of each of output values of the pair of line image sensors at a time when the line image sensors read the marker; and
driving means for driving in a direction of coinciding each of the overlapping portions of the pair of line image sensors with a sub scanning direction on the basis of the inspected result of the relative position.
Further, in accordance with the present invention, there is provided an image reading apparatus characterized in that the image corresponding to the marker changes a width in the main scanning direction.
In order to achieve the object, in accordance with the present invention, there is provided an image forming apparatus structured such that light sources of the image forming apparatus are arranged in a zigzag manner so that end portions of the light sources overlap with each other with respect to a scanning axis, and a light beam is irradiated onto an image surface of the paper from the light sources arranged in a zigzag manner.
Accordingly, it is possible to irradiate the light beam in a zigzag manner from both sides of the scanning axis, obtain a sufficient quantity of light with respect to a large-size paper and read a good image.